Dear Everyone,
Stop listening to stupid people. If someone's opinions/beliefs have no grounding in reality do not listen to them.
Theres no real evidence for the effectivness of masks in general public places. That many people have been told and believe there is, is not factual evidence of their effectiveness. Mostly they seem to be in use because they look like something is being done.
I cannot give case studies form anywhere else because i am in the UK. So...
There are two possibilites, either most of the Uk has had the virus, or relatively few have. We do not know which is the case. There was no effective testing to see who was infected at the time they were. Antibodies do not give a reliable measurement of amount of disease (most likely we do not normally zap the virus with antibodies, so it is very unreliable in ascertaining exposure. However, if people are constantly exposed to virus they will slowly develop an antibody response. Though they may never ever get symptoms)
In the first case, we have all had it anyway, the epidemic is essentially over, and masks are quite pointless. Its over folks, lets just get back to work.
In the second case it means the virus was never as infectious as commonly believed. Other evidence from contact tracing of people with the disease has shown that most infected people pass it on to precisely zero others. Actual spread is by relatively few people passing it to many others, or to mass spreading events. Examples are parties, bars, probably crowded public transport. Spread person to person depends critically how close you get. The risk is very small further than 1m apart. Masks irrelevant because the risk is very small anyway. Somewhere between there and touching the risk goes up hugely, It is not linear. If you are in range the risk is huge, and masks even if they cut that by a modest percentage make little real difference. If you got that close to someone infected, the mask will not help.
Experience tells us that normally walking round shops does not transmit the disease. Because if it did, we would all have caught it by now (see first case). If we never catch it from shopping, there is no point wearing a mask to reduce the risk.
The one time in the Uk we might have caught it in a supermarket was in the weeks before lockdown when government told people to stock up on food. Supermarkets were crammed solid. If people ever caught it there, then they did so then, following government advice, and just in time to create the big spike of cases seen around start of April in the UK. It is possible the peak of the epidemic in the Uk was created by government anti epidemic measures. (also it seems likely the policy of clearing hospitals of existing patients sent infected people into care homes, therby causing most of the deaths)
medics have shown masks alone will not stop spread in care homes or hospitals. You have to take lots of other measures as well. Most of all to make very sure no one with the virus ever goes into a care home. Hard to do that in hospitals, and that presumably is why UK hospitals have become a hotbed of catching covid. Probably same in US. As an example, a common pattern in Uk is six bed wards. They found patients were giving it each other, so cut out the middle beds. I'd guess that leaves beds a minium of 6ft/2m apart, more like 6m between the head of each patient. And then they use all sorts of washing, disinfecting, aprons, visors, space suits, whatever. Just a mask isnt going to hack it, and acually is supposed not to stop you catching it at all. Just reduce the amount you breathe out a bit.